Image forming apparatus with rotary element opposite an image reading unit

ABSTRACT

An image forming apparatus includes a sheet transport path that transports a sheet on which an image has been recorded, the sheet transport path including a first guide surface and a second guide surface opposed to the first guide surface, an image reading unit disposed on the same side as the first guide surface of the sheet transport path to read the image, and a rotary element disposed on the same side as the second guide surface, the rotary element being rotatably disposed with a gap between the rotary element and the first guide surface.

This is a reissue application of U.S. Pat. No. 9,733,615, which wasfiled as U.S. patent application Ser. No. 15/132,719 on Apr. 19, 2016and issued on Aug. 14, 2017, which claims priority to Japanese PatentApplication No. 2015-224371 filed Nov. 17, 2015, the disclosures ofwhich are incorporated herein by reference in their entireties.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 fromJapanese Patent Application No. 2015-224371 filed Nov. 17, 2015.

BACKGROUND Technical Field

The present invention relates to an image forming apparatus.

SUMMARY

According to an aspect of the invention, there is provided an imageforming apparatus including a sheet transport path that transports asheet on which an image has been recorded, the sheet transport pathincluding a first guide surface and a second guide surface opposed tothe first guide surface, an image reading unit disposed on the same sideas the first guide surface of the sheet transport path to read theimage, and a rotary element disposed on the same side as the secondguide surface, the rotary element being rotatably disposed with a gapbetween the rotary element and the first guide surface.

BRIEF DESCRIPTION OF THE DRAWING

Exemplary embodiments of the present invention will be described indetail based on the following figures, wherein:

FIG. 1 is a schematic cross-sectional view illustrating the generalinternal configuration of an image forming apparatus;

FIG. 2 is a schematic cross-sectional view illustrating the generalinternal configuration of a sheet discharge device;

FIG. 3 is a schematic cross-sectional view of the major components of asheet discharge device.

FIGS. 4A and 4B are respectively a bottom view and a schematiccross-sectional view of the imaging side of an imaging part;

FIGS. 5A and 5B are respectively a schematic plan view and a side viewof an upper guide plate including an imaging part;

FIGS. 6A and 6B are respectively a schematic plan view and a side viewof a lower guide plate including an opposed roller;

FIG. 7 is a schematic cross-sectional view illustrating the generalinternal configuration of a sheet discharge device;

FIG. 8 is a schematic cross-sectional view of a cooling part, a sheettransport part, a sheet bending part, and an image reading part; and

FIGS. 9A and 9B are plan views respectively illustrating an example ofpatch patterns used for tone correction, and an example of a ladderpattern of a test image.

DETAILED DESCRIPTION

Next, the present invention will be described in further detail withreference to the figures by way of its exemplary embodiments andspecific examples. However, the present invention is not limited to theexemplary embodiments and specific examples.

It is to be noted that in the following description made with referenceto the figures, the figures are for illustrative purposes only, anddetails such as the relative ratios of various dimensions may differfrom the actuality. For the ease of understanding, components other thanthose required for explanation are not illustrated as appropriate.

First Exemplary Embodiment

(1) Overall Configuration and Operation of Image Forming Apparatus

(1.1) Overall Configuration of Image Forming Apparatus

FIG. 1 is a schematic cross-sectional view illustrating the generalconfiguration of an image forming apparatus 1 according to a firstexemplary embodiment. The image forming apparatus 1 includes an imageforming part 10, a paper feed device 20 attached to one end of the imageforming part 10, a sheet discharge device 30 disposed at the other endof the image forming part 10 to discharge a sheet that has been printed,an operational information part 40, and an image processing part 50 thatgenerates image information from print information transmitted from ahost apparatus.

The image forming part 10 includes a system controller (notillustrated), exposure devices 12, photoconductor units 13, developingdevices 14, a transfer device 15, sheet transport devices 16a and 16b, afixing device 17, and an image reading device. The image forming part 10receives image information from the image processing part 50, and basedon the image information, the image forming part 10 forms a toner imageon a sheet of paper fed from the paper feed device 20.

The paper feed device 20 includes multiple paper loading parts (Tray1and Tray2) to receive sheets that differ in type (for example, material,thickness, paper size, and paper grain). The paper feed device 20supplies a sheet sent out from one of the multiple paper loading partsto the image forming part 10.

The sheet discharge device 30 discharges a sheet on which an image hasbeen formed in the image forming part 10. An image reading part 330 isdisposed further downstream of the fixing device 17 in the sheettransport direction. The image reading part 330 has the function ofreading image information recorded on a side of the sheet discharged andtransported from the fixing device 17 on which a toner image has beenformed.

The operational information part 40 is used to make various settings,input instructions, and display information. That is, the operationalinformation part 40 corresponds to a so-called user interface.Specifically, the operational information part 40 is made up of acombination of a liquid crystal display panel, various operatingbuttons, a touch panel, and other components.

(1.2) Configuration and Operation of Image Forming Unit

In the image forming apparatus 1 described above, a sheet sent out froma paper loading part of the paper feed device 20 that is specified by aprint job for each single sheet to be printed, is fed to the imageforming part 10 in synchronism with the timing of image formation.

The photoconductor units 13 are disposed in parallel below thecorresponding exposure devices 12. Each of the photoconductor units 13includes a photoconductor drum 131 that is rotationally driven. Acharger 132, the exposure device 12, the developing device 14, a firsttransfer roller 152, and a cleaning blade are disposed in the directionof rotation of the photoconductor drum 131.

The developing device 14 has a developing housing 141 in which adeveloper is received. A developing roller 142, which is opposed to thephotoconductor drum 131, is disposed inside the developing housing 141.A layer regulating member (not illustrated) that regulates the layerthickness of developer is disposed in close proximity to the developingroller 142.

Each of the developing devices 14 is of substantially the sameconfiguration except for the developer received in the correspondingdeveloping housing 141. Each of the developing devices 14 forms a tonerimage of yellow (Y), magenta (M), cyan (C), or black (K).

As the photoconductor drum 131 rotates, its surface is charged by thecharger 132, and an electrostatic latent image is formed on the surfaceof the photoconductor drum 131 by latent image-forming light emittedfrom the exposure device 12. The electrostatic latent image formed onthe photoconductor drum 131 is developed as a toner image by thedeveloping roller 142.

The transfer device 15 includes an intermediate transfer belt 151, thefirst transfer roller 152, and a second transfer belt 153. Theintermediate transfer belt 151 is a first endless belt to which tonerimages of various colors formed on the photoconductor drums 131 of thephotoconductor units 13 are transferred in a superimposed manner. Thefirst transfer roller 152 sequentially transfers toner images of variouscolors formed in the photoconductor units 13 to the intermediatetransfer belt 151 (first transfer). The second transfer belt 153 is asecond endless belt that transfers toner images of various colorstransferred onto the intermediate transfer belt 151 in a superimposedmanner, to a sheet that is a recording medium at once (second transfer).

The second transfer belt 153 is stretched under tension between a secondtransfer roller 154 and a stripping roller 155. The second transfer belt153 is sandwiched between a backup roller 165 disposed on the back sideof the intermediate transfer belt 151, and the second transfer roller154, forming a second transfer part (TR).

Toner images of various colors formed on the photoconductor drums 131 ofthe photoconductor units 13 are sequentially electrostaticallytransferred (first transfer) onto the intermediate transfer belt 151 bythe first transfer roller 152 that is being applied with a predeterminedtransfer voltage from a power supply device (not illustrated) controlledby the system controller. This first transfer forms superimposed tonerimages with various colors of toner superimposed on each other.

As the intermediate transfer belt 151 circulates, the superimposed tonerimages on the intermediate transfer belt 151 are transported to thesecond transfer part TR where the second transfer belt 153 is disposed.Once the superimposed toner images are transported to the secondtransfer part TR, a sheet is supplied to the second transfer part TRfrom the paper feed device 20 in synchronism with this timing. Then, apredetermined transfer voltage is applied to the backup roller 165,which is opposed to the second transfer roller 154 with the secondtransfer belt 153 therebetween, from the power supply device or otherdevices controlled by the system controller. This causes thesuperimposed toner images on the intermediate transfer belt 151 to betransferred to the sheet at once.

Residual toner on the surface of the photoconductor drum 131 is removedby the cleaning blade, and collected in a waste-toner receiving part(not illustrated). The surface of the photoconductor drum 131 is chargedby the charger 132 again.

The fixing device 17 includes a fixing belt 17a in an endless form thatrotates in one direction, and a pressure roller 17b that contacts theperipheral surface of the fixing belt 17a and rotates in one direction.The press contact region between the fixing belt 17a and the pressureroller 17b forms a nip part (fixing region).

After a toner image is transferred to the sheet in the transfer device15, the sheet is transported to the fixing device 17 via the sheettransport device 16a. In this state, the toner image has not been fixedonto the sheet yet. The toner image is then fixed onto the sheettransported to the fixing device 17 with pressure and heat applied bythe pair of the fixing belt 17a and the pressure roller 17b.

The sheet with the fixed toner image is fed to the sheet dischargedevice 30. When an image is to be formed on both sides of the sheet, thefront and back sides of the sheet are reversed by the sheet transportdevice 16b, and then the sheet is fed to the second transfer part TR ofthe image forming part 10 again. Then, after a toner image istransferred and the transferred image is fixed onto the sheet, the sheetis fed to the sheet discharge device 30. The sheet fed to the sheetdischarge device 30 is cooled in a cooling part 320. Then, after theimage on the sheet is read by the image reading part 330 as necessary,the sheet is discharged to a discharged-sheet receiving part (notillustrated).

(2) Configuration and Operation of Sheet Discharge Device

FIG. 2 is a schematic cross-sectional view illustrating the generalinternal configuration of the sheet discharge device 30. FIG. 3 is aschematic cross-sectional view of the major components of the sheetdischarge device 30. FIGS. 4A and 4B are respectively a bottom view anda schematic cross-sectional view of the imaging side of an imaging part331. FIGS. 5A and 5B are respectively a schematic plan view and a sideview of an upper guide plate 333 including the imaging part 331. FIGS.6A and 6B are respectively a schematic plan view and a side view of alower guide plate 334 including an opposed roller 335. FIGS. 9A and 9Bare plan views respectively illustrating an example of patch patterns PPused for tone correction, and an example of a ladder pattern of a testimage.

Hereinafter, the configuration and operation of the sheet dischargedevice 30 will be described with reference to the figures.

(2.1) Configuration of Sheet Discharge Device

As illustrated in FIG. 2, the sheet discharge device 30 includes a pairof receiving rollers 310, the cooling part 320, which is an example of acooling unit, the image reading part 330, a sheet bending part 340,which is an example of a bending unit, a sheet transport part 350, and apair of discharge rollers 360.

The sheet that has undergone fixing of a toner image and heating in thefixing device 17 is taken into the sheet discharge device 30 by the pairof receiving rollers 310. As the sheet passes through the cooling part320 along the side on which a curl has formed, heat is dissipated fromthe sheet. Then, the image reading part 330 optically reads an imageformed on the sheet cooled in the cooling part 320, and generates imagedata. Thereafter, the sheet has its curl straightened out in the sheetbending part 340 before being discharged to the discharged-sheetreceiving part (not illustrated) via the pair of discharge rollers 360.

As illustrated in FIG. 3, the cooling part 320 includes a cooling drum321, a transport belt 322, and a blower fan 325 (see FIG. 2). Thecooling drum 321, which is an example of a heat dissipation element,comes into contact with one side of the sheet. The transport belt 322 isstretched under tension so as to sandwich the sheet between thetransport belt 322 and the cooling drum 321. The blower fan 325, whichis an example of an air blower, blows a stream of air onto the coolingdrum 321 and the transport belt 322.

The cooling drum 321 is a cylindrical body entirely made of a metallicmaterial with high thermal conductivity, such as aluminum. In the firstexemplary embodiment, the cooling drum 321 is an aluminum pipe with adiameter of 200 mm. Support shafts 321a projecting from both ends of thecooling drum 321 are rotatably supported on a housing (not illustrated)of the sheet discharge device 30 via a bearing (not illustrated).

The transport belt 322 is, for example, an endless belt fabricated usinga synthetic resin material such as polyimide. The transport belt 322 issupported by a driving roller 323 and multiple support rollers 324 so asto circulate while being stretched under a predetermined tension. Thedriving roller 323 includes a base 323a in a cylindrical or circularcylindrical form made of a rigid material such as synthetic resin ormetal, and a covering layer (surface layer) 323b made of urethane resinor other materials coated on the peripheral surface of the base 323a forincreased friction with the inner peripheral surface of the transportbelt 322.

The blower fan 325 is rotationally driven during operation of thecooling part 320 to blow a stream of air onto the surfaces of thecooling drum 321 and the transport belt 322, thus cooling the coolingdrum 321 and the transport belt 322.

The sheet transport part 350 includes a transport path 351 that guidesthe sheet having passed through the cooling part 320 to the imagereading part 330, and a pair of transport rollers 352 that transportsthe sheet to the image reading part 330.

The image reading part 330 includes the imaging part 331, a photosensor332, the upper guide plate 333, and the lower guide plate 334. Theimaging part 331, which is an example of an image reading unit, isdisposed opposite to a side of the transported sheet on which an imagehas been formed, and reads the image on the sheet. The photosensor 332,which is an example of a detector, detects a test image. The upper guideplate 333 forms a first guide surface that guides the sheet duringtransport of the sheet. The lower guide plate 334, which is an exampleof a second guide surface, is disposed opposite to the upper guide plate333.

As illustrated in FIGS. 4A and 4B, the imaging part 331 is an in-linesensor (ILS) that optically detects an image fixed on the sheet, andmultiple patch patterns PP (PP1, PP2, PP3, PP4, PP5, PP6, PP7, PP8, PP9,PP10: see FIG. 9A) used for tone correction and for in-plane colorunevenness correction. The imaging part 331 is secured onto the innerside of the upper guide plate 333 by a holding member 336 such that theimaging part 331 is opposed to a surface of the transported sheet onwhich an image has been formed.

The imaging part 331 includes an irradiation part 331A, and a chargecoupled device (CCD) sensor 331B. The irradiation part 331A, whichincludes, for example, a linear tungsten lamp (not illustrated), ispositioned opposite to a surface of the sheet on which an image has beenformed. The CCD sensor 331B receives light radiated from the irradiationpart 331A and reflected by the sheet.

The imaging part 331 described above captures an image formed on thesheet being transported, and creates a spectrum in the wavelength rangeof, for example, 400 nm to 700 nm to take a color measurement of atarget area on the sheet. The resulting optical signal detected by theimaging part 331 is converted into an electrical signal. The electricalsignal is then transmitted to the system controller and used as data fortone correction and color unevenness correction.

The photosensor 332 has a light-emitting part 332a that emits light, anda light-receiving part 332b capable of receiving light emitted from thelight-emitting part 332a. The photosensor 332 optically reads a ladderpattern (see FIG. 9B) formed as a test image. The read signal istransmitted to the system controller, and used as, for example, data forcontrolling the transport speed of the sheet.

As illustrated in FIGS. 5A and 5B, the upper guide plate 333 is aplate-like member made of metal. The upper guide plate 333 includes afirst guide part 333A, a second guide part 333B, and a third guide part333C. The first guide part 333A guides the sheet toward the imaging part331. The second guide part 333B guides the sheet, which is transportedbelow the imaging part 331, along a light guide part 331a of the imagingpart 331. The third guide part 333C guides the sheet from which an imagehas been read in the imaging part 331, to the sheet bending part 340.

The second guide part 333B includes an opening 333Ba, an opening 333Bb,and an opening 333Bc. The opening 333Ba allows light radiated from theimaging part 331 to pass through the opening 333Ba, and guides lightthat is reflected in the direction of the optical axis by the imagesurface. The opening 333Bb allows light emitted from the light-emittingpart 332a of the photosensor 332 to pass through the 333Bb. The opening333Bc guides reflected light received by the light-receiving part 332b.

As illustrated in FIGS. 6A and 6B, the opposed roller 335, which is anexample of a rotary element, is disposed on the lower guide plate 334 soas to be opposed to the light guide part 331a of the imaging part 331,with the surface of the opposed roller 335 projecting from the lowerguide plate 334. The opposed roller 335 is disposed at a positionopposite to the light guide part 331a of the imaging part 331 and at aposition opposite to the photosensor 332, and is also disposed outsidethe area of the imaging part 331 in a direction that crosses (orthogonalto) the direction of transport of the sheet.

The opposed roller 335 is made of synthetic resin such as polyacetal(POM). The opposed roller 335 is an integral assembly of a main bodypart 335a in a cylindrical form, and a shaft part 335b extending fromeach end of the main body part 335a. The shaft part 335b is replaceablyattached to the lower guide plate 334.

The opposed roller 335 has a surface color that is selected inaccordance with a predetermined trigger image in a test image.Specifically, if the trigger image is the background portion (white) ofa ladder pattern formed as a test image, black is selected as thesurface color of the opposed roller 335, and if the trigger image is theimage portion (black) of the ladder pattern, then white is selected asthe surface color of the opposed roller 335.

The sheet bending part 340 is made up of a pair of decurling membersincluding an upper decurling member 340A and a lower decurling member340B that are opposed to each other so as to sandwich the transportedsheet therebetween. The pair of decurling members including the upperdecurling member 340A and the lower decurling member 340B includes atransport belt 341, which is supported by a driving roller 342 andmultiple support rollers 343 and 344 so as to circulate while beingstretched under a predetermined tension, and a pair of straighteningrollers 345 that press the transport belt 341 from the inner side of thetransport belt 341.

In the first exemplary embodiment, the straightening roller 345 of thelower decurling member 340B is in contact with one side of the transportbelt 341 of the upper decurling member 340A with the transport belt 341of the lower decurling member 340B therebetween. The straighteningroller 345 of the lower decurling member 340B bends the one side of thetransport belt 341 of the upper decurling member 340A upward tostraighten out an upper curl of the transported sheet that has been setin the cooling part 320.

A stream of air is blown from a blower fan 346 (see FIG. 2) onto thetransport belt 341 of the lower decurling member 340B. This allows heatto be dissipated from the sheet through the transport belt 341 of thelower decurling member 340B, thus securely fixing the straightenedposition imparted to the sheet. The sheet with its upper curl thusstraightened out is discharged to the discharged-sheet receiving part(not illustrated) from the pair of discharge rollers 360.

(2.2) Operation of Sheet Discharge Device

In the sheet discharge device 30 described above, after a toner image isfixed onto the sheet in the fixing device 17, the sheet is bent (curled)in the same direction as the side of the sheet on which the image to beread by the image reading part 330 is recorded, and then the sheet istransported to the cooling part 320 in that state.

In the cooling part 320, the sheet becomes sandwiched between thecooling drum 321 and the transport belt 322, and as the sheet istransported along the surface of the cooling drum 321, the sheet has itsheat removed by the cooling drum 321, causing the sheet to cool.

The sheet cooled in the cooling part 320 is guided to the image readingpart 330 via the sheet transport part 350. As the sheet passes throughthe gap defined between the second guide part 333B of the upper guideplate 333 where the imaging part 331 and the photosensor 332 aredisposed, and the opposed roller 335 disposed so as to project from thelower guide plate 334 toward the second guide part 333B, an imagerecorded on the surface of the sheet is read.

In the image reading part 330, the sheet, which has been cooled to alower temperature in the cooling part 320, is transported so as to passthrough the gap defined between the upper guide plate 333 and theopposed roller 335 with flopping of the sheet reduced, thus allowing foraccurate reading of the image recorded on the sheet.

The sheet with the image read in the image reading part 330 is guidedfrom the third guide part 333C to the sheet bending part 340.

In the sheet bending part 340, the straightening roller 345 of the lowerdecurling member 340B, which is in contact with one side of thetransport belt 341 of the upper decurling member 340A with the transportbelt 341 of the lower decurling member 340B therebetween, bends the oneside of the transport belt 341 of the upper decurling member 340A upwardto straighten out an upper curl of the transported sheet that has beenset in the cooling part 320. The sheet with its upper curl straightenedout is discharged to the discharged-sheet receiving part (notillustrated) from the pair of discharge rollers 360.

Second Exemplary Embodiment

FIG. 7 is a schematic cross-sectional view illustrating the generalinternal configuration of a sheet discharge device 30A. FIG. 8 is aschematic cross-sectional view of the cooling part 320, the sheettransport part 350, the sheet bending part 340, and the image readingpart 330.

Hereinafter, the configuration and operation of the sheet dischargedevice 30A will be described with reference to the figures. The sheetdischarge device 30A differs from the sheet discharge device 30according to the first exemplary embodiment in that the image readingpart 330 is disposed downstream of the sheet bending part 340 in thesheet transport direction. Accordingly, components that are the same asthose of the sheet discharge device 30 according to the first embodimentwill be denoted by the same reference signs, and a detailed descriptionwill not be given of those components.

As illustrated in FIG. 7, the sheet discharge device 30A includes thepair of receiving rollers 310, the cooling part 320, which an example ofa cooling unit, the sheet bending part 340, which is an example of abending unit, the image reading part 330, which is an example of animage reading unit, the sheet transport part 350, and the pair ofdischarge rollers 360.

As illustrated in FIG. 8, the sheet is taken into the sheet dischargedevice 30A by the pair of receiving rollers 310, and as the sheet passesthrough the cooling part 320 along the side on which a curl has formed,heat is dissipated from the sheet. The sheet is then transported to thesheet bending part 340 via the sheet transport part 350, and has itscurl straightened out in the sheet bending part 340.

Then, the image reading part 330 optically reads an image formed on thesheet that has been cooled in the cooling part 320 and has its curlstraightened out in the cooling part 320, thus generating image data.Thereafter, the sheet is discharged to the discharged-sheet receivingpart (not illustrated) via the pair of discharge rollers 360.

The foregoing description of the exemplary embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

What is claimed is:
 1. An image forming apparatus comprising: a sheettransport path configured to transport a sheet on which an image hasbeen recorded, the sheet transport path including a first guide surfaceand a second guide surface opposed to the first guide surface; an imagereading unit disposed on a same side as the first guide surface of thesheet transport path and configured to read the image, the image readingunit includes a light-emitting part to emit light; and a cylindricalrotary element disposed on a same side as the second guide surface, thecylindrical rotary element being rotatably disposed with a an air gapbetween the cylindrical rotary element and the first guide surface,along a full length of the cylindrical rotary element, when the imagereading unit reads the image, wherein the first guide surface includes alight passing part configured to allow light emitted from thelight-emitting part pass through, wherein the cylindrical rotary elementis disposed overlapping the light passing part in a direction oftransport of the sheet in the sheet transport path, and wherein thecylindrical rotary element is disposed in an area opposite to the imagereading unit in a direction perpendicular to a surface of thetransported sheet.
 2. The image forming apparatus according to claim 1,wherein the cylindrical rotary element is disposed in an area oppositeto the image reading unit, and disposed in an area that is not oppositeto the image reading unit in a direction that crosses a direction oftransport of the sheet.
 3. The image forming apparatus according toclaim 2, further comprising a detector that detects a test image formedon the sheet being transported, wherein the cylindrical rotary elementis disposed opposite to an area in which the test image is detected bythe detector.
 4. The image forming apparatus according to claim 1,further comprising a detector that detects a test image formed on thesheet being transported, wherein the cylindrical rotary element isdisposed opposite to an area in which the test image is detected by thedetector.
 5. The image forming apparatus according to claim 4 3, whereinthe test image includes a predetermined trigger image, and thecylindrical rotary element has a surface color that is selected inaccordance with the predetermined trigger image.
 6. The image formingapparatus according to claim 1, wherein the cylindrical rotary elementis removably disposed on the second guide surface.
 7. The image formingapparatus according to claim 1, further comprising a cooling unit thatcools the sheet, the cooling unit being disposed upstream of the imagereading unit in a direction of transport of the sheet in the sheettransport path.
 8. The image forming apparatus according to claim 7,wherein the cooling unit includes a heat dissipation element thatcontacts one side of the sheet being transported, an endless belt thatcirculates with the sheet sandwiched between the endless belt and theheat dissipation element to transport the sheet, and an air blower thatblows air onto the heat dissipation element and the endless belt.
 9. Theimage forming apparatus according to claim 1, further comprising abending unit that bends the sheet, the bending unit being disposeddownstream of the image reading unit in a direction of transport of thesheet in the sheet transport path.
 10. The image forming apparatusaccording to claim 1, further comprising a bending unit that bends thesheet, the bending unit being disposed upstream of the image readingunit and downstream of a cooling unit in a direction of transport of thesheet in the sheet transport path.
 11. The image forming apparatusaccording to claim 1, wherein the cylindrical rotary element includes aplurality of cylindrical rotating elements each separated by a gap alonga rotating axis of the cylindrical rotary element.
 12. The image formingapparatus according to claim 11, wherein the second guide surfaceincludes a plurality of openings, each of the cylindrical rotatingelements projecting through a corresponding one of the openings.
 13. Theimage forming apparatus according to claim 11, further comprising aphotosensor configured to read a pattern on the sheet, the photosensoraligned with one of the cylindrical rotating elements and the imagereading unit aligned with a different one of the cylindrical rotatingelements.
 14. The image forming apparatus according to claim 1, whereinthe cylindrical rotary element is fixed with respect to the first guidesurface to maintain the gap.
 15. The image forming apparatus accordingto claim 1, wherein the second guide surface approaches the first guidesurface along the sheet transport path in the transport direction. 16.The image forming apparatus according to claim 1, wherein the firstguide surface extends along the sheet transport path.